Current State of Extraction Don t Be Deceived! Sharon F. Webb, Ph.D. Director of Quality Program

Overview Factors Purpose of Dissolution Quality Objectives of Program Effectiveness of Dissolution Technique Safety Considerations Cost &/or Time Efficiency Generation of Waste Interferences Method of Detection

But First Remember! Support of AOAC 2017.02 Fertilizer Subgroup of the Agricultural Materials Community in AOACI History of Methods Forum Most using methods deriving from environmental methodologies Fertilizer matrices high salts, spectral interferences, uncontrolled ionization effects IRON SUIP No. 25 AOAC 2006.03

Method Requirements Equipment & instrumentation common in state fertilizer laboratories ICP-OES (not ICP-MS) Detection limits to meet SUIP #25 Digestion equipment & cross contamination requirements Extension of AOAC 2006.03 for nutritive metals Simple acid mixture, not perchloric acid Include wide variety of metals & fertilizer matrices, some sacrifices worth the expanded scope

Techniques Fusion Wet Ashing Acid Leaching Microwave Digestion Dry Ashing Considerations Solubility Rules g/100 ml solvent Soluble, slightly soluble, insoluble Solubility Constant: K sp As K sp, insolubility Exchange, decomposition, & Rearrangement Reactions Oxidation-Reduction Complexation

Fusion Combine flux (a salt) & sample Organic material ashed prior to this Crucibles: Pt, Zr, Ni, or porcelain Sand or oil baths on hot plate, furnace or burner Heat above melting point of salt, sample reacts with molten salt Dissolved cool fused sample Multiple times Multiple salts, acids, or combination Sample must contain chemically bound oxygen Moisture removed

Common Fluxes & Crucibles

Sulfate: Ignited oxides to sulfates Alkali-OH: Silicates, oxides, phosphates, fluorides, actinides in soils Na 2 CO 3 : silicates, refractory oxides, phosphates, & sulfates (K sp is high) Boron: Sand, slag, Al silicates, alumina, Fe, rare earth ores, Zirconium dioxide, Ti, niobium, Tantalum (Pt crucible) nasty Fluoride: silicon, destruction of silicates, rare earth metals; oxides of niobium, tantalum, Ti, Zi (Pt crucible) NaOH: Fe in soil Wet/Dry Ash: may leave oxides, silicates, nitrides, carbides, borides if looking for radionuclide

Common & Nasty Acids

Remember the Acids Oxidizing acids: metals whose E 0 > E 0 H

Standard reduction potentials of ½ reactions at 25 C

Remember the Acids HNO 3 : most commonly used HCl: most commonly used; insoluble silicates, ignited oxides of Al, Be, Cr, Fe, Ti, Zr or Th; oxides of Sn, Sb, Nb, Ta; Zr phosphate; sulfates of Sr, Ba, Ra, or Pb; alkaline earth fluorines; sulides of Hg; ores of Nb, Ta, U, or Th Aqua Regia: (1:3, HNO 3 :HCl) oxidizing effect of N +5 & Cl - coupled with catalytic effect of Cl 2 & NOCl acidity meets complexing power of Cl -! H 2 SO 4 : silicates not good for high concentrations of Ca, Sr, Ba, Ra, Pb HF: Dissolves silica & other silicates loves complexing; dissolves compounds of elements from IV to VI groups. Very NASTY! HClO 4 : hot, concentrated to be effective; attacks all metals but Au & Pt group metals; violent reactions; DANGEROUS higher probability to explode! Not contact organic material! No cotton!

Microwave Digestion Faster Cleaner More reproducible More accurate Time Efficient Open-Vessel Systems Low-Pressure, Closed Vessel System High-Pressure, Closed Vessel System Use up to 3 grams

AOAC Method Title--Solvents Matrix or element 965.09 Nutrients (Minor) in Fertilizers a HCl Inorganic materials & mixed fertilizers b Char, HCl Organic c HClO 4 /HF or HCl/HF Fritted trace elements d Mn: 972.02, 940.02, 941.02, 972.03 e H 2 O, EDTA Fe, Zn 949.02 Boron (Acid-Soluble) in Fertilizers ~17:1 H 2 O:HCl 949.03 Boron (Water-Soluble) in Fertilizers H 2 O ppt SO 4 & PO 4, boil out NH 3 titrate *NA >5% urea or urea-formaldehyde 982.01 Boron (Acid-and Water-Soluble) a 4:1 H 2 O:HCl b H 2 O, HCl added (1 ml HCl/95 ml H 2 O) 945.03 Calcium (Acid-Soluble) in Fertilizers 3:1 HNO 3 :HCl ppt Ba & Sr 965.10 Calcium (Acid-Soluble) in Fertilizers 945.03 Filter from Mg method (CaC 2 O 4 ) 937.01 945.04 Calcium (Acid-Soluble) in Fertilizers 965.09 965.11 Cobalt in Fertilizers H 2 SO 4, HNO 3, HClO 4 975.01 Copper in Fertilizer 965.09 941.01 Copper in Fertilizer HNO 3 & H 2 SO 4 ~1.5:1 942.01 Copper in Fertilizer HNO 3 & H 2 SO 4 2:01 NH 4 HF 2 967.01 Iron in Fertilizers 957.02B(e) HNO 3, HClO 4 HCl 980.01 Iron in Fertilizers 965.09

AOAC Method Title--Solvents Matrix or element 984.01 Magnesium (Acid-Soluble) 965.09 964.01 Magnesium (Acid-Soluble) a 2:1 HNO 3 :HCl, HClO 4 organic materials b 2:1 HNO 3 :HCl, HClO 4 Inorganic materials & mixed fertilizers 937.01 Magnesium (Acid-Soluble) 3:1 HNO 3 :HCl 940.01 Magnesium (Acid-Soluble) 937.01 filtrate H 2 SO 4 937.02 Magnesium (Water-Soluble) a H 2 O KMgSO 4, MgSO 4, kieserite b H 2 O Other material, mixed fertilizers c a or b extract 964.01D 972.02 Manganese (Acid-Soluble) a 940.02 Mn 2+ only 965.09D b 965.09C Mn 2+ & Mn 4+ 965.09D 940.02 Manganese (Acid-Soluble) 3:1 HNO 3 :H 2 SO 4, HNO 3, H 3 PO 4 941.02 Manganese (Acid-Soluble) 7:1 H 2 SO 4 :HNO 3, HNO 3 972.03 Manganese (Water-Soluble) ROH, H 2 O, H 2 SO 4 Mn 2+ only 974.01 Sodium in Fertilizers 955.06 H 2 O & (NH 4 ) 2 C 2 O 4 983.04 Sodium in Fertilizers H 2 O & (NH 4 ) 2 C 2 O 4 942.02 Zinc in Fertilizers ~1:5 H 2 SO 4 :HNO 3, HNO 3, H 2 O 942.03 Zinc in Fertilizers 1:1 HNO 3 :H 2 SO 4, HNO 3, H 2 O 975.02 Zinc in Fertilizers 965.09 973.01 Zinc in Fertilizers 1:2 HNO 3 :HCl, HCL 2006.03 As, Cd, Co, Cr, Pb, Mo, Ni, & Se HNO 3, Microwave 2017.02 As, Ca, Cd, Co, Cr, Cu, Fe, Pb, Mg, Mn,Mo, Ni, & Se in Fertilizers 3:1 HNO 3 :HCl

Acid Leaching or Total Dissolution? How much dissolution determines the data Fusion is more labor intensive Large quantities of flux required up to 5 to 10 times the sample weight Possible contamination from large amounts of flux Higher temperature requirements increases safety concerns Mineral acids are effective for metals, oxides and salts in most fertilizers

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